Electron storage rings operating at an energy near 1 GeV (one billion electron volts) are typically used as light sources producing X-rays or UV light. The electron storage rings are oblong, re-entrant, loop structures in which bunches of electrons circulate, emitting synchrotron radiation whenever they are bent into a curved path. The energy lost by the electrons through radiation is replaced by passing them through radio frequency (RF) accelerating cavities which restore the lost electron energy.
Such electron storage rings are typically injected with electrons of energies considerably lower than the operating energy of the ring because of the cost and size of a full-energy injector of electrons. For example, a known prior art device operates at 700 MeV (million electron volts) and is injected at 200 MeV by an electron linac. This linac, essentially a series of RF cavities, is 36 meters long and costs about four million dollars to build. Roughly, cost and length scale linearly with energy. A 1 GeV electron linac would cost twenty million dollars and be 180 meters long.
Reduced energy injection of an electron storage ring produces several problems. First, the beam lifetime at reduced energies is only a few minutes. As a result, the beam must be injected quickly and a reduced-energy injector must supply a lot of electrons (100 milliamps at 10 Hertz). Second, the storage ring must be ramped to full energy within these few minutes to minimize loss of electrons. This restricts the design of the storage ring's bending magnets. These are subject to both eddy currents, hysteresis, and time-changing loads. Third, the storage ring is unusable while it is being injected and ramped to full energy.
A great advance would occur if a constant-energy, full-energy storage ring could be made practical through a cheap method of full-energy injection. This would allow full-energy storage rings to be simpler in construction and cheaper to build and permit the use of permanent magnets in place of the conventional electromagnets used in these prior art machines. Further, this would eliminate the need for the huge power supplies and cooling systems necessary to operate prior art storage ring devices.